Many patients that suffer from congestive heart failure (CHF) develop a wide QRS complex resulting from a delayed activation of one of the ventricles in the heart, and inter- and/or intraventricular electrical-mechanical dysynchrony. This ventricular “dysynchrony” may be caused by dilation of the heart, which disrupts the conductive pathways and interferes with depolarization sequences. Ventricular dysynchrony may worsen heart failure symptoms.
In a classic case of ventricular dysynchrony, the patient's right ventricle activates first, and the left ventricle activates at a later time. The patient often experiences a reduction in cardiac output because the ventricles begin contraction at significantly different times. The timing imbalance may also cause the patient to experience paradoxical septal motion, mitral regurgitation or decreased ventricular filling time.
Patients having a wide QRS complex or having inter- and/or intraventricular electrical-mechanical dysynchrony may receive benefits from an implanted medical device, such as a pacemaker, that paces both ventricles. The implanted medical device senses or paces atrial contractions, waits a predetermined time (or atrioventricular (AV) delay) after each sensed or paced atrial contraction, and then paces both ventricles. The ventricles may be paced simultaneously, or one ventricle may be paced before another. This bi-ventricular pacing is one form of cardiac resynchronization, and it provides many CHF patients with improvements in quality of life, exercise capacity and overall cardiac function.
Generally speaking, cardiac resynchronization refers to pacing therapies applied by implanted medical devices with one or more pacing leads in two or more complementary chambers of the heart. For purposes of the following discussion, the right and left atria are complementary to one another, and the right and left ventricles are complementary chambers. The right and left atria are complementary because they are the upper chambers that receive blood and transfer it to the ventricles. The right and left ventricles are complementary chambers because they receive blood from the atria and pump the blood to the heart. In a heart in a healthy patient, complementary chambers activate at approximately the same time. In a heart in a patient suffering from a condition such as CHF, complementary chambers activate at different times.
In response to a sensed or paced event, the pacemaker delivers pacing pulses or stimulations to two complementary chambers of the heart. The pacing pulses may be, but need not be, delivered simultaneously. Although the discussion that follows emphasizes bi-ventricular pacing to treat ventricular dysynchrony, cardiac resynchronization also encompasses, for example, resynchronization of atrial contractions.
Multiple-chamber pacing systems in general, and bi-ventricular and bi-atrial pacing systems in particular, are known in the art. Prior art techniques for synchronizing ventricles or atria are generally imprecise, however, and are not adaptive to changing conditions. In a typical bi-ventricular pacemaker that delivers pacing pulses to the ventricles at different times, for example, the time interval between delivery of the pacing pulses may be fixed and not automatically adjustable.
Examples of these techniques and/or devices may be found in the issued U.S. patents listed in Table 1 below.
TABLE 1U.S. Pat. No.InventorIssue Date4,485,813Anderson et al.Dec. 4, 19845,158,078Bennett et al.Oct. 27, 19926,070,101Struble et al.May. 30, 20006,081,748Struble et al.Jun. 27, 20006,122,545Struble et al.Sep. 19, 20006,144,880Ding et al.Nov. 7, 2000
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.